In many instances, it is desirable to detect changes in a reflective element. Such changes are caused for example by a particular wetting of a surface, effected in order to derive control commands for closing windows or other openings for example, or for removing an interfering wetting. For example, an inner reflection surface of a radiation-permeable plate or wall (inner or total reflection), a mirror, or any other means, which possibly also reflects only stray light, can be considered as a reflecting element, such as, for example, a hand approaching the arrangement. The term wetting of a surface is understood to mean the covering or sprinkling of the surface with individual drops of liquid or the striking of drops of liquid against the surface, until a liquid film or foam is deposited on the surface, or until a liquid layer of a particular layer thickness has accumulated on the surface.
By means of the detection of the extent of the change of reflection ratios it is possible, for example, to detect the position changes or the appearance of an object, which moves or can be moved in front of the arrangement. If the change is a wetting, then concerted control commands can be derived, for example by means measuring of the quantity of the wetting liquid per unit of surface area and/or per unit of time on the wetted surface, by means of which, for example, the wetting can be regulated, closing events can be controlled as a function of the existing or expected quantity of liquid or an operation for removing the wetting can be optimally controlled as a function of the history of the cause of the wetting.